This application relates to optical signal multiplexers, and in particular, to optical signal multiplexers and demultiplexers based on evanescent coupling through a polished fiber coupling port.
Optical waves may be transported through optical waveguiding elements or xe2x80x9clight pipesxe2x80x9d such as optical fibers, or optical waveguides formed on substrates. A typical fiber may be simplified as a fiber core and a cladding layer surrounding the fiber core. The refractive index of the fiber core is higher than that of the fiber cladding to confine the light. Light rays that are coupled into the fiber core within a maximum angle with respect to the axis of the fiber core are totally reflected at the interface of the fiber core and the cladding. This total internal reflection provides a mechanism for spatially confining the optical energy of the light rays in one or more selected fiber modes to guide the optical energy along the fiber core. Optical waveguides formed on substrates can also be designed to provide spatial optical confinement based on total the internal reflection. Planar waveguides, for example, may be formed by surrounding a slab or strip of a dielectric material with one or more dielectric materials with refractive indices less than that of the dielectric slab or strip.
Optical fibers may be used in transmission and delivery of optical signals from one location to another in a variety of optical systems, including but not limited to, fiber devices, fiber links and fiber networks for data communications and telecommunications. Optical waveguides on substrates may be used in integrated optical devices where optical elements, opto-electronic elements, or MEMS elements are integrated on one or more substrates.
The guided optical energy in the fiber or waveguide, however, is not completely confined within the core of the fiber or waveguide. In a fiber, for example, a portion of the optical energy can xe2x80x9cleakxe2x80x9d through the interface between the fiber core and the cladding via an evanescent field that essentially decays exponentially with the distance from the core-cladding interface. The distance for a decay in the electric field of the guided light by a factor of e≈2.718 is about one wavelength of the guided optical energy. This evanescent leakage may be used to couple optical energy into or out of the fiber core, or alternatively, to perturb the guided optical energy in the fiber core.
This application includes optical devices having at least one fiber integrated on or engaged to a substrate fabricated with one or more grooves. One portion of the cladding of this fiber is removed and polished to form a fiber coupling port through which optical energy can be evanescently coupled into or out of the fiber core via evanescent fields. At least two such fiber coupling ports may be formed at different positions in the fiber such that this fiber can be coupled with two coupling ports of another fiber or planar waveguide to form a Mach-Zehnder interferometer for signal processing operations such as optical attenuation, optical modulation, optical switching, and signal multiplexing or demultiplexing.
The fiber may be mounted and engaged to one or more grooves formed in a substrate in a fiber device. One embodiment includes a substrate that is formed with an elongated groove on one substrate surface, and at least one opening located at one end of the groove that penetrates through the substrate. An optical fiber is engaged to the substrate by passing through the opening to lay a portion in the groove. The fiber cladding of the portion in the groove may be partially removed to form a fiber coupling port to allow for evanescent coupling.
The optical coupling between a fiber in a first substrate in one of the above fiber devices and a waveguide formed in a second substrate may be implemented by positioning the first and the second substrates relative to each other so that a coupling port of the fiber is adjacent to the waveguide to allow for evanescent coupling between the fiber and the waveguide. A single fiber may be optically coupled to two or more waveguides through its different coupling ports located in grooves of the first substrate.